PROTECTING GUAM’S CORAL REEFS BY IMPROVING SCUBA DIVER BEHAVIOR: A CORAL-SAFE DIVING REMINDER REDUCES REEF CONTACTS BY ASHTON N. WILLIAMS A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN BIOLOGY SUPERVISORY COMMITTEE Dr. Laurie Raymundo, Chair Dr. Alexander Kerr, Member Dr. Romina King, Member UNIVERSITY OF GUAM DECEMBER 2019 Abstract Coral reefs are a critical resource for the culture and economy of the American territory of Guam, but the island’s coral reef resources are increasingly imperiled by climate change, particularly bleaching caused by rising seawater temperatures. Severe bleaching events in 2013, 2014, 2016, and 2017 have caused mass mortality of corals and made evident the critical need to reduce local stressors to protect the future of Guam’s reefs. An estimated 300,000 people scuba dive on Guam’s reefs annually, but the impacts of these divers are unknown. This study examines the impacts of scuba diving activity on highly trafficked coral reefs and tests a low-effort approach to reducing diver impacts by using a coral-safe diving reminder. Comparisons of benthic cover, genus diversity, and health impacts did not reveal any significant differences between pairs of often dived and rarely dived sites, although it is likely that the damage and mortality caused by recent bleaching events may be masking the smaller impacts of scuba divers. A single-sentence coral-safe diving reminder delivered as part of the standard pre-dive briefing was highly effective in reducing both accidental and intentional contacts with reef. Divers who received a coral-safe diving reminder made 72% fewer contacts with the reef, and about 60% fewer contacts with live corals specifically, than divers who did not receive a reminder. Predictors of high-impact divers were identified, including camera users, gloves users, visiting divers, large groups, and poor buoyancy control. The results of this study may be used by diving professionals to identify potential high-impact divers who may benefit from increased supervision. Based on the results of this study, recommendations for reducing the impacts of scuba divers on coral reefs are presented for dive operators, regulating bodies, and individual divers. 2 Acknowledgements I would first and foremost like to thank my thesis advisor, committee chair, and dear friend Dr. Laurie Raymundo, for her endless patience and unwavering support over the last few years. I would also like to thank my thesis committee members, Dr. Alex Kerr and Dr. Romina King, for their patience, advice, and positive attitudes throughout this project. I must also thank Ms. Whitney Hoot for generously volunteering her time to assist with my research. I would like to thank the faculty, staff, and students (both present and past) at the University of Guam Marine Laboratory: Diona Drake, Alisha Gill, and Jessica DeBlieck for being excellent dive buddies; Dive Safety Officer John Peralta for his commitment to keeping me alive; Jason Miller for his sparkling personality; Angie Duenas for being an amazing administrative goddess; Nicole Burns for her friendship and emotional support; Marylou Staman for convincing me to come to Guam; Jordan Gault and James Fifer for their invaluable assistance in my darkest hours in R; and everyone else at the Marine Lab for their friendship, support, and commiseration. I must extend my sincere gratitude to Mr. Lee Webber and Captain Bill of Micronesian Divers Association for their cooperation with this study. I would like to thank Captain Todd Genereaux for his cooperation and boating expertise. I also owe thanks to the Guam Visitors Bureau for funding for this project and providing visitor data. I would like to thank the National Park Service for employing me while I worked on this thesis, particularly my fellow interns Ms. Nina Peck and Ms. Maria Lynn Cruz, and of course Mr. Michael Gawel for his support, advice, and approval of my flexible work schedule. I must also thank my family for never giving up on me (by which I mean never ceasing to ask if I had graduated yet); my fearless feline companions, Evie & River, for constant cuddles and excellent conversation; and my Nespresso machine. And finally, thank you for reading the fruits of my labor. Cheers! 3 Table of Contents Abstract ..................................................................................................................................... 2 Acknowledgements .................................................................................................................. 3 Table of Contents ..................................................................................................................... 4 List of Tables ............................................................................................................................ 7 List of Figures ........................................................................................................................... 8 1. Introduction .......................................................................................................................... 9 1.1 Coral reefs in decline ....................................................................................................... 9 1.2 Reducing local stressors through stakeholder participation ........................................... 10 1.3 Scuba diver impacts on coral reefs ................................................................................ 15 1.4 Scuba diving on Guam ................................................................................................... 19 1.5 Diver impact studies ...................................................................................................... 23 1.6 Hypotheses ..................................................................................................................... 30 2. Methods ............................................................................................................................... 31 2.1 Overview ........................................................................................................................ 31 2.2 Coral-safe diving reminder ............................................................................................ 31 2.2.1 Coral-safe reminder delivery .................................................................................. 32 2.2.2 Diver observations .................................................................................................. 32 2.2.3 Site selection ........................................................................................................... 33 2.2.4 Analysis................................................................................................................... 35 2.3 Coral health surveys ....................................................................................................... 35 2.3.1 Site selection ........................................................................................................... 35 2.3.2 Survey methods ....................................................................................................... 36 2.3.3 Analysis................................................................................................................... 37 2.3 Predictors for high-impact divers................................................................................... 37 2.3.1 Observational data .................................................................................................. 38 2.3.2 Questionnaires......................................................................................................... 38 2.3.3 Analysis................................................................................................................... 40 2.4 Additional analyses ........................................................................................................ 41 3. Results ................................................................................................................................. 42 3.1 Coral-safe diving reminder ............................................................................................ 42 3.1.1 Diver-reef contacts .................................................................................................. 43 3.2 Coral health surveys ....................................................................................................... 46 3.2.1 Community composition ......................................................................................... 46 3.2.2 Benthic cover .......................................................................................................... 47 3.2.3 Health impacts ........................................................................................................ 52 4 3.3 Predictors of high-impact divers .................................................................................... 54 3.3.1 Guide/client correlation .......................................................................................... 55 3.3.2 Group size ............................................................................................................... 56 3.3.3 Site Type ................................................................................................................. 57 3.3.4 Demographic predictors .......................................................................................... 58 3.3.5 Diving experience, activity,